J.K. Simmons was reluctant to star in 'Being the Ricardos'.

The 67-year-old actor plays William Frawley in Aaron Sorkin's movie – which delves into the relationship between the 'I Love Lucy' stars Lucille Ball (Nicole Kidman) and Desi Arnaz (Javier Bardem) – but needed "reassurance" before taking on the part.

J.K. told Variety: "I wasn't all that interested, despite Aaron's involvement. I've always been reluctant to portray real people, especially 20th century people who have been in the public eye."

Simmons then recalled how Aaron reassured him that "mimicry" wasn't needed for the role.

He said: "That was all the reassurance I needed to get over my fear. It was a scary prospect for all four of us to play these iconic people. Obviously I'm very glad I did the film."

The Spider-Man star revealed how he wanted to do justice to William Frawley and got a friend to give him as much information as possible about the late actor.

Simmons explained: "I wanted to honour William Frawley – who he was and wasn't. So it was a different kind of preparation than I usually do. To me, the inner life is what's paramount. I worked on that, and it was important to get at the heart of who he was.

"I think we all have at least one friend who's an absolute nerd for all things 'I Love Lucy'. Alan Filderman, a New York casting director who's a friend, called and said, 'I have six books you need to read and I want to tell you everything I know about William Frawley'. That's where my research started."

Simmons revealed how Alan gave him some valuable insights about Frawley that he could apply to his performance.

He recalled: "Alan told me Bill Frawley's hands often shook. As I watched old episodes, I realised that whenever you see him standing there, he's protecting his hands. He's got his hands in pockets, or folded in front of him, hands firmly on hips. He never lets himself be vulnerable, by letting the audience see his hands shake."